With regard to freight railways overseas, in order to achieve high efficiency in railway transportation, a carrying capacity of freight loads has been improved. In particular, in rails used for a section through which a large number of trains passes or for sharp curves, significant wear occurs on a head top portion or a head corner portion of the rail (the periphery of corner of the rail head which intensely contacts with flange portions of wheels). Therefore, there is a problem of a reduction in the service life due to an increase in the amount of wear.
In addition, similarly, in a domestic passenger rails, particularly, in the rail used for sharp curves, the wear progresses remarkably as in the freight railways overseas, so that there is a problem in that the service life is reduced due to an increase in the amount of wear.
From this background, the development of a rail with high wear resistance is required. In order to solve the problem, a rail as described in Patent Document 1 has been developed. The main characteristic of the rail is that its pearlite structure (lamellar spacing) is made finely by performing a heat treatment in order to increase the hardness of the pearlite structure.
In Patent Document 1,a technique of performing a heat treatment on a steel rail containing high-carbon steel so as to cause the metallic structure to have a sorbite structure or a fine pearlite structure. Accordingly, by achieving a high hardness of the steel rail, it is possible to provide a rail with excellent wear resistance.
However, in recent years, further carrying capacity and further high speed of trains of freight loads has been improved for the freight railways overseas and the domestic passenger rails in order to further achieve high efficiency in railway transportation. In the rail described in Patent Document 1, it becomes difficult to ensure the wear resistance of the head portion of the rail, so that there is a problem in that the service life of the rail is greatly reduced.
Here, in order to solve the problem, a steel rail with a high carbon amount has been considered. This rail has characteristics such that the wear resistance is enhanced by increasing the volume ratio of cementite in the lamellae of the pearlite structure (for example, refer to Patent Document 2).
In Patent Document 2, a rail which has a pearlite structure as its metallic structure by enhancing a carbon amount of the steel rail to a hypereutectoid region is disclosed. Accordingly, the wear resistance is enhanced by increasing the volume ratio of a cementite phase in the pearlite lamellar, so that a rail with higher service life can be provided. According to the rail described in Patent Document 2, the wear resistance of the rail is enhanced, so that an improvement of definite service life is achieved. However, in recent years, an excessive increase in the density of railway transportation has been progressed, so that the generation of fatigue damage from the head portion or the bottom portion of the rail exists. As a result, although the rail described in Patent Document 2 is used, there is a problem in that the service life of the rail is not sufficient.
Citation List
[Patent Literature]
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. S51-002616
[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H08-144016
[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. H08-246100
[Patent Document 4] Japanese Unexamined Patent Application, First Publication No. H09-111352